Magnetic disk drive

ABSTRACT

A plurality of patterns are formed beforehand so that each of those patterns is deviated slightly from another in each sector in the track width direction, then the pattern is followed up, thereby obtaining both full-track profile and micro-track profile. A variation of a position signal is detected from this profile, thereby creating a table for correcting the non-linearity error of the position signal.  
     Consequently, the distribution of the write/read-back property is measured, thereby enabling the track density to be improved. Furthermore, a variation of the position signal caused by a property variation of the head read-back element is detected and corrected, thereby enabling a high reliability and a high track density to be realized for the object magnetic recording disk apparatus.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to an information recordingapparatus provided with a magnetic conversion head and a magneticrecording medium, more particularly to a magnetic recording diskapparatus that has improved its track density.

[0002] Generally, in order to make a head follow up an object data trackon a magnetic recording disk medium, the magnetic recording diskapparatus must enable relative positional information between the headand the magnetic recording disk medium to be kept measured accuratelyand a positional deviation caused by a thermal expansion differencebetween both magnetic recording disk medium and the arm that supportsthe head, as well as an influence of such a disturbance as rotationvibration of the spindle motor and the rotary actuator to be reduced.This is why special patterns for positioning the head are recorded onthe magnetic recording disk medium before the shipping. The area inwhich such a pattern is recorded as shown in FIG.6 is referred to as aservo area 31. The servo area 31 is formed between data areas 33 via agap area 32. After the shipping, it is inhibited that the user recordsdata in this servo area 31. In the servo area 31 is recorded datacontinuously between adjacent tracks 16 in the radial direction. Theservo track width 311 is equal to the track pitch of the tracks 16. Onthe other hand, in a data area 33, recorded data on each track 16 isseparated from another. The recording track width 331 is narrower thanthe track pitch of the tracks 16. Actually, 60 to 100 servo areas 31 areformed at equal pitches on a round of track 16 of the magnetic recordingdisk medium.

[0003] FIG.7 shows a configuration of such a servo area 31. An ISG part40 is a continuous pattern provided so as to reduce the influence of thedistribution of the magnetic property in the recording film and thedistribution of the flying height of the magnetic recording disk medium.The servo decoder circuit reads back the ISG part 40 by turning on theauto gain control (AGC). Upon detecting an AM part 41, the AGC is turnedoff, thereby the magnetic recording disk apparatus of the presentinvention normalizes the read-back amplitude of the subsequent burstparts 43 with the amplitude of the ISG part 40. A gray code part 42describes the track number information of each track 16 with a graycode. This part 42 often describes sector number information, as well.The burst part 43 makes a houndstooth check pattern for obtainingaccurate positional information in the radial direction. This part 43 isindispensable for following up the center of each track 16 accurately.This pattern 43 consists of a pair of A-burst 43-1 and B-burst 43-2 thatare provided as straddle the center of each track 16 alternately, aswell as C-burst 43-3 and D-burst 43-4 that are provided as straddle theedge of each track 16 alternately. A pad part 44 is a pattern providedso as to absorb the delay of the decoder circuit system to keepgenerating a clock while the servo decoder circuit reads back the servoarea 31.

[0004] The head 11 reads back the servo areas 31 while running on theposition C shown with an arrow from left to right in FIG. 7. FIG. 8(A)shows an example of the read-back waveform at that time. To simplify thedescription, the read-back waveforms of the AM part 41, the gray codepart 42, and the pad part 44 are omitted here. The servo decoder circuit44 detects the amplitudes of the four burst parts (from the A-burst part43-1 to the D-burst part 43-4). The amplitude value of each burst partis converted to a digital value in the AD converter, then entered to aCPU. The CPU then calculates the difference between the amplitudes ofthe A-burst part 43-1 and the B-burst part 43-2, thereby finding the Nposition signal. Although an equation for normalizing the differencewith the amplitude of the ASG part 40 is described in FIG. 7, thisfunction is realized by hardware in which the servo decoder circuitlocks the AGC so as to fix the amplitude of the ISG part 40. In the sameway, the CPU obtains the Q position signal from the difference betweenthe amplitude values of the C-burst part 43-3 and the D-burst part 43-4.FIG. 8B shows the position signals of the head, which are generated asdescribed above. The N position signal becomes 0 at a position where thecenter of the head 11 straddles the A-burst part 43-1 and the B-burstpart 43-2 equally. The N position signal becomes positive or negativealmost in proportion to a deviation from this center position. Forexample, the N position signal at the position C shown in FIG. 8B can beobtained from the read-back waveform shown in FIG. 8(A) at the positionC shown in FIG. 7. Usually, it is assumed that the edges of both A-burstpart 43-1 and B-burst part 43-2 match with the center of each track 16.

[0005] The CPU inverts the status (positive/negative) of the N or Qposition signal, whichever is smaller in absolute value, then links thesignals, thereby generating a continuous position signal. This positionsignal is then compared with a target position, thereby finding anoptimal current value to be applied to a voice coil motor 14 so as toperform such predetermined operations as following-up and seeking.

[0006] A technique for forming a spiral data track itself is disclosedin Japanese Published Unexamined Patent Application No.62-204476,No.63-112874, and No.61-296531 respectively. A technique for formingspiral servo information itself is disclosed in FIG. 1 of JapanesePublished Unexamined Patent Application No.62-204476.

BRIEF SUMMARY OF THE INVENTION

[0007] The above conventional techniques, however, have been confrontedwith a problem that non-uniformity of the direction of magnetization inthe read-back element degrades the linear accuracy of the positionsignal, thereby the radial position of the head cannot be controlledaccurately. In addition, those conventional techniques have also beenconfronted with a problem that because the detection accuracy of theposition signal is degraded by a property variation of the read-backelement, the radial position of the head cannot be-controlledaccurately.

[0008] In the recent years, however, it is common that a high readsensitivity head is used to increase the recording density of the objectmagnetic recording disk apparatus. For example, there are well-knowntechniques for using a read-back head that employs a magnetoresistiveelement (MR element) that makes good use of the magnetoresistive effectof the magnetic film itself, a giant magnetoresistive element (GMRelement) that has improved the magnetoresistive effect with anon-magnetic film sandwiched by magnetic films, or a tunnelmagnetoresistive element (TMR element) that has improved themagnetoresistive effect more with use of a phenomenon that a tunnelcurrent is changed by an external magnetic field significantly. Thosetechniques are all effective, since each of those magnetoresistiveelements can obtain a favorable SN ratio even in reading back finerecorded patterns on magnetic recording disks, thereby the bit densityof the object magnetic recording disk apparatus can be improved.

[0009] Generally, both ends of a magnetoresistive element are structuredso as to enable a bias magnetic field (vertical bias magnetic field) tobe applied in the width direction of the track, thereby forming themagnetic film of the element in a single magnetic domain structure.Consequently, the read-back sensitivity is degraded with respect to thestrength of the leakage magnetic field of the object disk at both endsof the element, thereby the output is not made in uniform in the widthdirection of the track. In addition, because the magnetizing directionis disturbed at both ends of the element, the amplitude value may differsignificantly between positive side and negative side of the read-backwaveform. And furthermore, the non-uniformity of the magnetizingdirection, which is a problem mentioned here, may be varied in variousforms due to the recording magnetic field generated by the write elementprovided adjacently to the magnetoresistive element. This phenomenon isreferred to as a property variation of the read-back element. Thisproperty variation of the read-back element may also occur due to achange of the flying attitude of the head caused by a wear, a flaw, anda contaminant thereon.

[0010] Because the read-back sensitivity is low at both ends of theelement, the read-back amplitude of the burst part 43 is notproportional to the radial position of the head. Both of N and Qposition signals also do not become proportional to the radial positionof the head exactly. If any asymmetrical component of the verticalamplitude is contained in the read-back waveform of the burst part 43,then the constant of the decoder circuit comes to depend on the positionsignal significantly, thereby the errors of both N and Q positionsignals become more serious. Because of those negative factors, the Nand Q position signals of the magnetic recording disk apparatus thatuses a magnetoresistive element do not become linear as shown in FIG.8B. There is a technique for improving the accuracy for detecting theerror level referred to as a non-linearity error of this position signalby creating a correction table and using the table. In this case,however, a correction table must be prepared for each head mounted inthe magnetic recording disk apparatus and the table must be recorded inthe memory of the package board 17 or in part of the management area onthe disk 12 before shipping. Consequently, the management of productionprocesses becomes complicated, and furthermore, the difference amongproperties of decoder circuits cannot be corrected even with thistechnique. Those factors have thus been an obstacle for the improvementof the track density of the apparatus.

[0011] Furthermore, the center of a track to follow up may be offset dueto a change of the non-linearity error level if a property variationoccurs in the read-back element. To avoid such a read-back error tooccur due to a change of the property variation of the read-backelement, therefore, a current is applied to the write element so as toexecute a dummy write operation that applies an external magnetic fieldto the read-back element intentionally, thereby eliminating the propertyvariation. This is a well-known technique. And yet, there is stillanother problem that must be solved. The problem is a fact that thecontent of the variation in a magnetized state differs between propertyvariation of the read-back element related to the nonlinearity of theposition signal and the property variation of the read-back elementrelated to a read-back error. The technique that performs a dummy writeoperation after a read-back error occurs cannot avoid a possibility thatan offset from a target track, thereby overwriting is done on anadjacent track. This has been a factor for degrading the reliability ofthe magnetic recording disk apparatus.

[0012] This is why there has been expected appearance of a new techniquethat enables the non-linearity error of the position signal caused bythe read-back property of the head and the servo decoder circuitproperty to be corrected so as to improve the positioning accuracy,thereby detecting the property variation of the read-back elementrelated to the non-linearity error of the position signal and improvethe data track density of the magnetic recording disk apparatus thatemploys a magnetoresistive element as the read-back element. It is thuspossible to prevent the fatal error that overwrites data on adjacenttracks so as to improve the reliability of the apparatus.

[0013] In order to achieve the above objects, the magnetic recordingdisk apparatus of the present invention comprises a magnetic recordingdisk medium provided with a plurality of tracks formed thereon in aconcentric circle pattern and a servo area formed on a part of eachtracks and used to record a servo pattern; a magnetic recording headprovided with a read-back element and a write element; and a servodecoder circuit for generating a head position signal from the servopattern formed on the magnetic recording disk medium; wherein aplurality of patterns are disposed in an area different from the servoarea on the disk medium. Each of a plurality of the patterns is deviatedfrom another in the radial direction of the track at least by a widthnarrower than the width of the read-back element of the head.

[0014] Furthermore, a plurality of full tracks are disposed in someradial areas on the disk so that each of the full tracks is deviatedslightly from another in the radial direction of the disk and theamplitude of the read-back waveform of each of those full tracks isdetected while following up the track, thereby measuring the profile ofeach full track from the amplitude of the read-back waveform.

[0015] Furthermore, in the magnetic recording disk apparatus of thepresent invention, a plurality of micro-tracks are disposed in someradial areas on the disk so that each of those micro-tracks is deviatedslightly from another in the radial direction of the disk and theamplitude of the read-back waveform of each of a plurality of themicro-tracks is detected while the track is followed up, therebymeasuring the profile of the micro-track from the amplitude of theread-back waveform.

[0016] The magnetic recording disk apparatus is provided with a functionfor calculating an effective write or read-back width of the head fromthe profile of the full-track or the micro-track. The magnetic recordingdisk apparatus is also provided with a function for correcting thenon-linearity of the head position signal from the profile of thefull-track or the micro-track. The magnetic recording disk apparatus isfurther provided with a function for detecting a variation of the headposition signal from the profile of the full-track or the micro-track.The magnetic recording disk apparatus is further provided with afunction for detecting a variation of the head read-back property fromthe profile of the micro-track. In addition, the magnetic recording diskapparatus is further provided with a function for correcting thevariation if the variation is out of a preset range.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017]FIG. 1 shows the first example of a pattern for detectionfull-track profile of the present invention.

[0018]FIG. 2 shows the second example of a pattern for detectionfull-track profile of the present invention.

[0019]FIG. 3 is a top view of a structure of a magnetic recording disk.

[0020]FIG. 4 is a cross sectional view of the structure of the magneticrecording disk.

[0021]FIG. 5 is a bottom view of part of the magnetic recording disk.

[0022]FIG. 6 is an explanatory view of a structure of a sector of themagnetic recording disk apparatus.

[0023]FIG. 7 is an explanatory view of a structure of a servo area ofthe magnetic recording disk apparatus.

[0024]FIG. 8 shows a process for calculating a position signal from aservo read-back waveform.

[0025]FIG. 9 shows a process for creating a pattern for detectionfull-track profile of the present invention.

[0026]FIG. 10 is a block diagram of a pattern detector circuit of thepresent invention.

[0027]FIG. 11 shows an example of a full-track profile detected from apattern of the present invention.

[0028]FIG. 12 shows the third example of the pattern for detectionfull-track profile of the present invention.

[0029]FIG. 13 shows the fourth example of the pattern for detectionfull-track profile of the present invention.

[0030]FIG. 14 shows the first example of a pattern for detectionmicro-track profile of the present invention.

[0031]FIG. 15 shows the second example of the pattern for detectionmicro-track profile of the present invention.

[0032]FIG. 16 shows an example of the micro-track profile detected froma pattern of the present invention.

[0033]FIG. 17 shows how to calculate an effective read-back width and aneffective write width of a head.

[0034]FIG. 18 shows an example of how to correct a head position signal.

[0035]FIG. 19 shows an example of how to detect and correct a variationof the head position signal from a full-track profile.

[0036]FIG. 20 shows an example of how to detect and correct a propertyvariation of a read-back element from a profile of a micro-track.

DESCRIPTION OF THE SYMBOLS

[0037]11 . . . Head 12 . . . Disk 13 . . . Rotary Actuator 14 . . .Voice Coil Motor 15 . . . Head Amplifier 16 . . . Track 17 . . . PackageBoard 31 . . . Servo Area 32 . . . Gap Part 33 . . . Data Area 40 . . .ISG Part 41 . . . AM Part 42 . . . Gray Code Part 43 . . . Burst Part 44. . . Pad Part 51 . . . Pattern for Detection Full-track Profile 52 . .. Pattern for Detection Full-track Profile 53 . . . Pattern forDetection Full-track Profile 54 . . . Pattern for Detection Full-trackProfile 55 . . . Micro Servo Area 56 . . . Pattern for DetectionMicro-track Profile 57 . . . Pattern for Detection Micro-track Profile

DETAILED DESCRIPTION OF THE INVENTION Embodiment 1

[0038]FIG. 3 shows a top inside view of an enclosure of a magneticrecording disk apparatus and FIG. 4 shows a cross sectional view of theapparatus. The main parts composing the magnetic recording diskapparatus are as shown in FIGS. 3 and 4, that is, six heads 11; threedisks 12; a rotary actuator 13; a voice coil motor 14; a head amplifier15; a package board 17, etc. The three disks 12 are fixed to a hub andeach of the disks 12 is rotated around the point A by a spindle motor.The six heads 11 are fixed to a comb-like arm and each of the heads 11is rotated around the point B by the rotary actuator 13. With thismechanism composed as described above, each head 11 can move freely inthe radial direction of the disk 12. In the package board 17 are mounteda central processing unit (CPU) used for controlling; a hard diskcontroller (HDC); an interface circuit; a memory; a signal processingunit, etc. Because the S/N ratio and the transfer rate are improved moreif the head amplifier 15 is disposed near to each head 11, the headamplifier 15 is not mounted on the package board 17; it is often mountedin the enclosure.

[0039]FIG. 5 shows a top partial view of the disk 12. Each head 11 isfixed at a radial position of any of data tracks 16-1, 16-2, . . . on adisk 12 by the rotary actuator 13 and used to write and read backinformation in and from the data tracks 16 electrically. Data tracks 16are formed at equal pitches in a concentric circle pattern.

[0040] Although only four data tracks 16-1 to 16-4 are shown in theexplanatory view in FIG. 5, there are more than 8000 data tracksactually formed at pitches of 2 μm or under on the disk 12.

[0041]FIG. 1 shows a configuration of a pattern for detection full-trackprofile 51, which is used to detect the profile of each full-track(provided with a width equal to the width of a recording track in a dataarea) in an embodiment of the present invention.

[0042] In FIG. 1, the horizontal direction indicates the circumferentialdirection of the disk 12 and the vertical direction indicates the radialdirection of the disk 12. Each head 11 moves both in the direction inwhich the head runs and in the direction shown with an arrow at a speedof 6 to 11m/sec relatively to the disk 12. In FIG. 1, an area assignedwith a sector number 1 is duplicated at both right and left sides. Thisis just appearance, because a one-round pattern on the disk 12 formed incircumference is drawn linearly. The areas on both right and left sidesare thus in one and the same sector 1 actually. The areas assigned witha sector number 72 are also in one and the same area actually. Someservo areas 31 shown in FIG. 1 are composed just like those described inthe related art. The magnetic recording disk apparatus composed asdescribed above are provided with 72 servo areas 31 formed at equalpitches on a round of the disk 12. A total of the 72 servo areas 31occupies a length of about 7% of a round of the disk 12. The track pitch(Tp) is 1.78 μm and the symbol 2×Tp shown in FIG. 1 means an equivalenceto 3.55 um.

[0043] A pattern for detection full-track profile 51 is recorded betweenservo areas 31. The pattern for detection full-track profile 51 is apattern having a width equal to that of the recording track 331 in eachdata area 33. In this configuration of the disk 12, the pattern fordetection full-track profile 51 is recorded as simple repetitivepatterns to be inverted at a 20 MHz clock. If this pattern 51 is readback from a track, the pattern 51 takes a waveform close to a 10 MHzsine wave. Unlike the pattern in a normal data area 33, it ischaracterized by the use of a simple magnetizing pattern. None of suchmagnetizing patterns as the PLL sink area, the data address mark, theECC, the CRC is not used.

[0044] The patterns for detection full-track profile 51 recorded in thearea whose sector numbers are 1 and 2 respectively are magnetizedpatterns having the same frequency, but they are deviated from eachother only by 0.05 μm in the radial direction of the disk. In addition,the patterns for detection full-track profile 51 recorded in the areaswhose sector numbers are 3 to 72 are deviated from each other only by0.05 μm sequentially in the same direction. Consequently, the patternsfor detection full-track profile 51 recorded in the areas whose sectornumbers are 1 and 72 are deviated from each other only by 3.55 μmsequentially in the radial direction of the disk. The 3.55 μm is doublethe track pitch.

[0045] Hereunder, a description will be made for a process for writingthe pattern shown in FIG. 1 described above with reference to FIG. 9. Inthe servo area writing process included in the manufacturing processescarried out in a factory, the pattern is written with use of amanufacturing apparatus referred to as a servo track writer. The servotrack writer uses an external laser measuring apparatus to drive therotary actuator 13 while measuring the position of each head 11accurately. At first, data is written in servo areas 31 entirely in thefull radius range of the disk 12. After that, control goes to theprocess for writing a pattern for detection full-track profile 51.

[0046]FIG. 9(A) shows a head 11 moved only by 0.05 μm in the radialdirection upto a position where a pattern for detection full-trackprofile 51 is recorded in an area whose sector number is 1, then anotherpattern for detection full-track profile 51 is recorded in an area whosesector number is 2. This state of the disk 12 indicates that the disk 12has been rotated once. FIG. 9B shows the state of the disk 12 after itis rotated twice. This state indicates that the head 11 is moved only by0.05 μm in the radial direction upto the next writing position after apattern for detection full-track profile 51 is written in the area whosesector number is 2. FIG. 9C shows a state of the disk 12 started atsector number 3 has just finished the pattern writing after 72 times ofrotation. Finally, the patterns for detection full-track profile 51written in the areas whose sector numbers are 1 and 72 are deviated fromeach other by 3.55 μm sequentially in the radial direction of the disk12. The time required for forming the 72 patterns described above, ifthe disk 12 is rotated at 400 rpm, is 72×0.015=1.08 s. In this case, itis premised that the disk 12 is rotated once at 0.015 s. On thecontrary, the time for forming a normal servo area 31 is

8000×2×0.015+8000×2×0.015×⅓=320 s

[0047] if the disk 12 is rotated at 400 rpm and servo writing is done on8000 tracks at ½ pitches and the disk is rotated by ⅓ while the head ismoved to an adjacent track. The time required for adding a pattern fordetection full-track profile 51 of the present invention is very slightwhen compared with the time required for a normal servo track writingprocess.

[0048]FIG. 2 shows a configuration of the pattern for detectionfull-track profile 52 as another embodiment of the present invention.The vertical direction in FIG. 2 is the radial direction of the disk 12and the pattern 52 consists of 72 servo areas just like in theconfiguration of the pattern 51 shown in FIG. 1. In FIG. 2, however, thetrack pitch (Tp) is 1.75 μm and the symbol 2×Tp shown in FIG. 2 means anequivalence to 3.5 μm.

[0049] The patterns for detection full-track profile 52 written in theareas whose sector numbers are 1 and 2 are magnetized patterns havingthe same frequency, but they are deviated from each other by 0.1 μm inthe radial direction of the disk. In addition, the patterns fordetection full-track profile 52 written in the areas whose sectornumbers are 3 to 35 are deviated from each another by 0.1 μmsequentially in the radial direction of the disk. The patterns fordetection full-track profile 52 written in the areas whose sectornumbers are 1 and 35 are deviated from each other only by 3.5 μmsequentially in the radial direction of the disk. The 3.5 μm is anequivalence to double the track pitch. In the area whose sector numberis 36 is written a pattern for detection full-track profile 52. The areais written in the same radial position as that of the area whose sectornumber is 1. In the same way, in the areas whose sector numbers are 37to 72 are written patterns for detection full-track profile 52 in thesame radial positions as those of the areas whose sector numbers are 2to 35.

[0050] The pattern 52 shown in FIG. 2, when compared with the pattern 51shown in FIG. 1, is deviated from another only by a half, so the profiledetecting accuracy also becomes a half. On the contrary, because thesame pattern is repeated twice while the disk is rotated once, the errorto be caused by the mechanical vibration when in writing and in readingback patterns can be reduced with employment of an averaging processing.It depends on the mechanical vibration content of the servo track writerand the spindle motor which pattern can detect the full-track profilemore accurately. Although the pattern described here is formed bydividing a 2×Tp track width by 36 within a range of ½-round of the disk,the track width, the disk rotation distance, and the dividing number canbe decided freely.

[0051]FIG. 10 shows a block diagram of a decoder circuit for detectingfull-track profiles from the pattern of the present invention.

[0052] In order to simplify the configuration, the decoder circuitsystem of the present invention is just composed by adding a band-passfilter (BPF), an amplifier (AMP), and a switch to the conventional servodecoder circuit. Read-back data output from a head 11 is amplified by100 to 200 times in the amplifier 15, then high frequency componentnoises are removed from the data with use of a low-pass filter (LPF).The auto gain controller (AGC), as described in the related art withreference to FIGS. 7 and 8, adjusts the amplitude of read-back waveformsso as to fix the amplitude of the ISG part 40. When the address markdetector (AM detector) detects the AM part 41 from a signal obtained byconverting a read-back waveform to a digital waveform in the peakdetector, the AGC is turned off to fix the amplified gain, thereby thedetecting accuracy of the pattern for detection full-track profile isprevented from non-uniformity of magnetic property of the disk andinfluence of the disk flying height.

[0053] The center frequency of the BPF is set to 10 MHz, which is thesame as the read-back frequency of the pattern for detection full-trackprofile, so that noise is removed from the signal component of thepattern, thereby the detecting accuracy is improved. The switch selectsthe BPF side when in detecting a full-track profile. When in detecting amicro-track profile to be described later, the switch selects theamplifier (AMP) side. The bit length of the pattern for detectionfull-track profile can be set longer than the burst part 43 in a normalservo area 31, so the integral time constant of the integrator is setlong according to the length of the pattern so as to improve thedetecting accuracy. The A/D converter converts the amplitude of thepattern detected by the integrator to a digital value. The centralprocessing unit (CPU) and the hard disk controller (HDC) are used tocontrol the timings of the AGC, the switch, the integrator, and the A/Dconverter.

[0054]FIG. 11(A) shows a case in which the pattern shown in FIG. 2 iswritten by a head 11 on a disk 12 built in a magnetic recording diskapparatus and a read-back amplitude is detected in each sector. In FIG.11 (A), the horizontal axis indicates sector numbers. Sector numbers 1to 72 are equivalent to sectors on a round of the disk. The verticalaxis indicates output values from the A/D converter that detects theamplitude of each sector. The read-back profiles 1 and 2 indicated withwhite and black circles are not the same, since they are influenced bythe mechanical vibration of the servo track writer when in writingpatterns and by the mechanical vibration of the spindle motor when inreading back patterns. FIG. 11B shows an average of the profiles 1 and 2shown in FIG. 11(A). In FIG. 11B, the horizontal axis indicates theaverage profile converted in units of um. When the radial position ofthe head exceeds the ±1.2 μm range, the output value becomes a value onthe noise level of the detection system. This profile is a full-trackprofile detected automatically on the disk built in the magneticrecording disk apparatus. The horizontal axis is calibrated with theaccuracy of the laser measuring apparatus of the servo track writer.

[0055]FIG. 12 shows a configuration of a pattern for detectionfull-track profile 53 as further another embodiment of the presentinvention. In order to improve the detecting accuracy, the pattern fordetection full-track profile 53 is multiplexed before it is written, sothat the pattern 53 enables an averaging processing to be performed asmany as possible. In FIG. 12, the vertical direction is the radialdirection of the disk 12 and the horizontal direction is thecircumferential direction of the disk 12. Although there is only oneservo area whose sector number is 1 in an expanded view in FIG. 12,there are actually 72 servo areas 31. The track pitch is 1.78 μm and thesymbol 2×Tp shown in FIG. 12 means an equivalence to 3.55 just like inthe configuration of the pattern shown in FIG. 1.

[0056] In order to multiplex each pattern for detection full-trackprofile 53 before it is written, the pattern length is set shorter thanthat shown in FIG. 1. This pattern is written by 72 times in an areawhose sector number is 1 so that each pattern is deviated from anotherby 0.05 μm sequentially in the radial direction of the disk.Consequently, the patterns at both start and end of each sector aredeviated from each other by 3.55 μm in the radial direction of the disk.The 3.55 μm is a length equivalent to double the track pitch. Inaddition, the same configuration pattern as that written in the areawhose sector number is 1 is thus written in the areas -whose sectornumbers are 2 to 72.

[0057] The pattern 53 shown in FIG. 12, when compared with the pattern51 shown in FIG. 1, can reduce the error occurrence caused by themechanical vibration when in writing and reading back patternssignificantly with execution of an averaging processing, since the samepattern is repeated by 72 times while the disk 12 is rotated once. Onthe other hand, because each pattern for detection full-track profile 53is short, this configuration arises problems that the pattern amplitudedetecting accuracy is degraded and a high accuracy is required forgenerating a clock from the detector. Although the pattern in thisembodiment is formed by dividing a 2×Tp track width by 72 within asector range, the track width and the dividing number may be decidedfreely.

[0058]FIG. 13 shows a configuration of a pattern for detectionfull-track profile 54 as further another embodiment of the presentinvention. In order to solve the problems of the configuration shown inFIG. 12 and improve the detecting accuracy more, the pattern ismultiplexed less in number and the number of servo areas is increased inthe configuration shown in this FIG. 13. In FIG. 13, the verticaldirection is the radial direction of the disk 12 and the horizontaldirection is the circumferential direction of the disk 12. Although onlythe servo areas whose sector numbers are 1 to 18 are shown in theexpanded view in FIG. 13, there are actually 72 servo areas 31. Thetrack pitch is 1.78 μm and the symbol 2×Tp shown in FIG. 13 means anequivalence to 3.55 just like in the configuration shown in FIG. 1.

[0059] Three micro-servo areas 55 are provided at equal pitches betweenservo areas respectively. The configuration of each micro-servo area 55is the same as that described in the related art with reference to FIG.7 except that the gray code part 42 is removed. A micro-servo area 55 isprovided only in a track width measuring zone. In a data zone where adata area 33 exists is provided only a normal servo area 31. The patternfor detection full-track profile 54 is provided in an area between aservo area 31 and a micro-servo area 55 or between micro-servo areas 55.In the sector number=1 area, four patterns for detection full-trackprofile can be disposed so that each pattern is deviated from another by0.05 μm sequentially in the radial direction of the disk. The fourthpattern for detection full-track profile in the sector number=1 area isdeviated by 0.05 μm from the first pattern for detection full-trackprofile in the sector number=2 area. In the same way, 72 patterns fordetection full-track profile 54 can be written in the areas whose sectornumbers are 1 to 18 sequentially. The first pattern for detectionfull-track profile in the sector number=1 area is deviated by 3.55 μmfrom the fourth pattern 54 in the sector number=18 area in the radialdirection of the disk. The 3.55 μm is an equivalence to double the trackpitch. In addition, the same configuration pattern as that written inthe areas whose sector numbers are 1 to 18 is written in the areas whosesector numbers are 37 to 54 and 55 to 72.

[0060] The pattern 54 shown in FIG. 13 is repeated four times while thedisk 12 is rotated once. These four patterns are averaged, thereby theerror caused by the mechanical vibration when in writing and readingback patterns can be reduced more than the embodiments shown in FIGS. 1and 2 in which patterns 51 and 52 are used. In addition, because eachpattern is extended and a micro-servo area 55 is provided, it ispossible to solve the problems related to the pattern amplitudedetecting accuracy and the clock generation accuracy of the detectorcircuit more than when the pattern shown in FIG. 12 is used. Although apattern is formed by dividing a 2×Tp track width by 72 within a range of¼ rotation of the disk in this embodiment, the track width, the diskrotation distance, and the dividing number may be decided freely.

[0061] According to the above embodiment, patterns for detectionfull-track profile on a disk built in the object magnetic recording diskapparatus can be detected automatically very accurately by reducing theerror occurrence caused by the mechanical vibration when in writing andreading back patterns with employment of the pattern configuration, thewriting process, and the detector circuit system as described in thisembodiment.

Embodiment 2

[0062]FIG. 14 shows a configuration of a pattern for detectionmicro-track profile 56, which is a pattern for detecting a micro-track(having a width narrower than that of the recording track in each dataarea) profile as an embodiment of the present invention. This patternconfiguration has many common items as the pattern for detectionfull-track profile 52 shown in FIG. 2. The pattern for detectionmicro-track profile 56 is a pattern having a width narrower than that ofthe recording track 331 in each data area 33. Just like the patternconfiguration shown in FIG. 2, this pattern configuration includes 72servo areas 31, the track pitch is 1.75 um, and the symbol 2×Tp means anequivalence to 3.5 um.

[0063] A pattern for detection micro-track profile 56 is written betweenservo areas 31 respectively. The pattern for detection micro-trackprofile 56 is formed with 20 MHz patterns repeated simply and having anarrow track width of not more than ¼ of the track width of the writeelement. Although the patterns for detection micro-track profile 56written in the areas whose sector numbers are 1 and 2 are magnetizedpatterns having the same frequency, they are deviated from each other by0.05 μm in the radial direction of the disk. In addition, the patternsfor detection micro-track profile 56 written in the areas whose sectornumbers are 3 to 72 are deviated by 0.05 μm from each anothersequentially in the radial direction of the disk. Consequently, thepatterns for detection micro-track profile 56 written in the areas whosesector numbers are 1 and 72 are deviated from each other by 3.55 μm inthe radial direction of the disk. The 3.55 μm means an equivalence todouble the track pitch.

[0064] To write the patterns for detection micro-track profile 56, amanufacturing apparatus referred to as a servo track writer is used inthe manufacturing processes in the object factory. This is to form thepattern 56 having a track width narrower than that of the write elementof the head very accurately. In order to form a pattern for detectionmicro-track profile 56, the disk must be rotated twice. At the firstrotation, a full track is written in the sector number=1 area with 20MHz patterns repeated simply, then the head is deviated by 0.3 μm inwardin the radial direction of the disk. In this state, it is awaited untilthe disk is rotated up to the sector number=1 area, then a DC current isapplied to the head in the sector number=2 area on the second rotationso as to erase the patterns written in the first rotation from one sideand form a pattern whose track width is narrower than that of the writeelement of the head. The width of the pattern for detection micro-trackprofile 56 formed actually is narrower than 0.3 μm deviated when inerasing. This is caused by a phenomenon that the width for the head toerase old data is wider than the width for the head to write new data.

[0065] Although the pattern described in this embodiment is formed bydividing the 2×Tp track width by 36 within a range of ½ rotation of thedisk, the track width, the disk rotation distance, and the dividingnumber may be decided freely.

[0066] It is possible to reduce the time for forming 72 patterns formicro-track profile by carrying out both write process at the firstrotation and erase process at the second rotation as described above atthe same head position. It does not need any time for rotating the diskby the number of times double the 72 patterns. For example, because thehead position where a pattern is erased from one side in the sectornumber=1 area is the same as the head position where a pattern iswritten in the sector number=7 area, these two write and erase processescan be carried out while the disk is rotated once. The use of thismethod will thus be able to reduce the time for forming 72 patterns fordetection micro-track profile upto a time for rotating the disk by6+72+6=84 times.

[0067] The configuration of the decoder circuit for detectingmicro-track profiles from the pattern of the present invention is almostthe same as that described above in the embodiment 1 with reference toFIG. 10. However, when compared with the read-back amplitude of afull-track, the read-back amplitude of a micro-track is as small asabout ⅓ to {fraction (1/10)}, so 3 to 10 times of amplifiers (AMP) aredisposed serially and the switch is set to AMP. Functions of othercomponents are the same as those in the embodiment 1.

[0068]FIG. 16(A) shows an example of detection of the read-backamplitude of a pattern for detection micro-track profile 56 shown inFIG. 14 in each sector. The pattern for detection micro-track profile iswritten by a head 11 on a disk 12 built in the object magnetic recordingdisk apparatus. The horizontal axis indicates sector numbers. Sectornumbers 1 to 72 are equivalent to the number of sectors on one round ofthe disk. The vertical axis indicates output values from the A/Dconverter that detects the amplitude of each sector. The profile 1indicated with white circles and the profile 2 indicated with blackcircles may not become identical sometimes due to the influence of themechanical vibration of the servo track writer when in writing of thepattern 56 or the mechanical vibration of the spindle motor when inreading back the pattern 56.

[0069]FIG. 16B shows an average of the read-back profiles 1 and 2 shownin FIG. 16(A). The value in the horizontal axis is converted to a valuein units of um. The output value, when the radial position of the headis within a range of ±1.1 um, is a value on the noise level of thedetection system. This profile is a micro-track profile detectedautomatically on the disk built in the magnetic recording diskapparatus. The horizontal axis is calibrated with the accuracy of thelaser measuring apparatus of the servo track writer.

[0070]FIG. 15 shows a configuration of a pattern for detectionmicro-track profile 57 as another embodiment of the present invention.In FIG. 15, the vertical direction is the radial direction of the disk12 and the horizontal direction is the circumferential direction of thedisk 12. The pattern for detection micro-track profile 57 has manycommon points to those of the, pattern for detection micro-track profile54 shown in FIG. 13. Just like in the configuration of the pattern 54shown in FIG. 13, there are a total of 216 micro-servo areas 55 only inthe track width measuring zone, the track pitch is 1.78 um, and thesymbol 2×Tp means an equivalence to 3.55 um. In FIG. 15, of the 72 servoareas 31, only the areas whose sector numbers 1 to 18 are shown in anexpanded view.

[0071] A pattern for detection micro-track profile 57 is written betweena servo area 31 and a micro-servo area 55 respectively. In order toimprove the detection accuracy more, the pattern 57 is multiplexed sothat the number of servo areas is increased.

[0072] Four patterns for detection micro-track profile can be disposedin the sector number=1 area so that each of them is written so as to bedeviated from another by 0.05 μm sequentially in the radial direction ofthe disk. The fourth pattern for detection micro-track profile in thesector number=1 area is also deviated by 0.05 μm from the first patternfor detection micro-track profile in the sector number=2 area. In thesame way, 72 patterns for detection micro-track profile can be writtensequentially in the areas whose sector numbers are 1 to 18. The firstpattern in the sector number=1 area is deviated by 3.55 μm from thefourth pattern in the sector number=18 area in the radial direction ofthe disk. The 3.55 μm is double the track pitch. In addition, the sameconfiguration pattern as that written in the areas whose sector numbersare 1 to 18 is written in the areas whose sector numbers are 19 to 36,37 to 54, and 55 to 72 respectively.

[0073] The pattern 57 shown in FIG. 15 is repeated four times while thedisk 12 is rotated once. Those four patterns 54 are averaged, therebythe error occurrence caused by the mechanical vibration when in writingor reading back patterns can be reduced more than when the pattern shownin FIG. 14 is used. In addition, because the pattern 57 is provided withmicro-servo areas 55, the pattern amplitude detection accuracy can beimproved more than when the pattern 56 shown in FIG. 14 is used.Although a pattern is formed by dividing the 2×Tp track width by 72within a range of ¼-round of the disk in this embodiment, the trackwidth, the disk rotation distance, and the dividing number may bedecided freely.

[0074] With the employment of the pattern configuration, the writingprocess, and the detector circuit system described in this embodiment,the present invention has made it possible to reduce the erroroccurrence caused by the mechanical vibration when in writing andreading back patterns, thereby enabling micro-track profiles on a diskbuilt in the object magnetic recording disk apparatus to be detectedvery accurately.

[0075] Next, a description will be made for a method for calculating aneffective read-back width and an effective write width from bothmicro-track profile and full-track profile described above withreference to FIG. 17.

[0076] The read-back profile from a micro-track having a width narrowerthan that of the write element track of the head matches with thesensitivity distribution profile of the head in the leakage magneticfield of the disk in the track width direction. Consequently, theread-back profiles from the satisfactorily narrow micro-track areintegrated, thereby each profile from the recording tracks in variousareas can be calculated.

[0077]FIG. 17(A) shows a normalized result of convolution integral ofthe micro-track profile shown in FIG. 16B and a step function with themaximum value. Because values not within a range of ±1.1 μm of themicro-track profile is noise level ones, they are removed by a simplesubtraction respectively. The horizontal axis in the graph correspondsto the radial position at the rising of the step function from 0 to 1.This profile matches with the read-back profile at one side from a varywide recording track. If the effective read-back width of the read-backhead is assumed to be a width that can output 5 to 95% of the read-backprofile at one side from the very wide recording track, the effectiveread-back width will be found to be 1.1 μm as shown in FIG. 17(A).

[0078] Each white circle shown in FIG. 17B is a full-track profile shownin FIG. 11B. The solid line indicates a result of normalization of theconvolution integral of the micro-track profile shown in FIG. 16B and arectangular function with the maximum value. Because values not within arange of ±1.1 μm of the micro-track profile are noise level ones, theyare removed by a simple subtraction respectively. In FIG. 17B, thehorizontal axis is shifted so as to match each calculation result withthe right side profile each time the rectangular function width ischanged to 1.3, 1.4, and 1.5 μm sequentially. Because the result ofintegrating by 1.4 μm matches with the measured full-track profile mostsatisfactorily, the effective write width will become 1.4 μm. Actually,it can be judged with the value of the root sum of the differencebetween both values whether or not the measured value matches with thecalculated value.

[0079] Next, a description will be made for a method for finding asensitivity correction coefficient of a head position signal from amicro-track or a full-track profile with reference to FIG. 18.

[0080]FIG. 18(A) shows that a curve (measured value(=A-burst)) is forfull-track profiles detected just like in the embodiment 1. This curvecan also be found by convolution integral of micro-track profilesperformed with use of a rectangular function, which is detected justlike in the embodiment 2. The (B-burst) curve is obtained by shifting ameasured value to the right (inner circumferential direction) accordingto a value that is the track pitch. These two curves are equivalent tothe A amplitude of A-burst 43-1 and the B amplitude of B-burst 43-2described in the related art with reference to FIGS. 7 and 8. Becausethe AGC is controlled so as to fix the amplitude of the ISG part 40,both A and B amplitudes are normalized with the ISG amplitude. Themeasured value curve shown in FIG. 18B indicates values obtained bysubtracting the B amplitude from this A amplitude respectively and it isequivalent to the N position signal shown in FIG. 18B. As described inthe PROBLEMS TO BE SOLVED BY THE INVENTION, this measured N positionsignal curve does not become a straight line in many cases.

[0081] In the case of the conventional magnetic recording diskapparatus, because the apparatus is controlled on the assumption thatthe value shown on the vertical axis in FIG. 18B is related to a trueposition proportionally, an error comes to occur in a radial position ofthe head. This error becomes a problem especially in an operationreferred to as a micro-jog that corrects an offset between the read-backelement and the write element. The offset between the read-back elementand the write element is changed according to the yaw angle of theslider, so the N position signal must match with an ideal straight lineshown in FIG. 18B at a given radial position of the head. In addition,the change of the position signal with respect to the radial position ofthe head is lowered at a position near to the linkage between N and Qposition signals, so the servo loop gain is further lowered as the valueof ±0.6 μm comes closer in FIG. 12B. The positioning accuracy is thusdegraded. These errors are referred to as non-linearity errors ofposition signals.

[0082]FIG. 18C shows a value obtained by dividing an ideal line by ameasured line. The value can be used as a sensitivity correctioncoefficient of position signals. This coefficient is multiplied by aposition signal detected by the servo decoder circuit, thereby enablingthe nonlinearity error occurrence of the above position signal to bereduced significantly. The sensitivity correction coefficient of theposition signal found here is written beforehand in the memory of thepackage board 17 or in part of the management area of the disk 12 foreach head.

[0083] The burst part 43 of the servo area 31 is usually formed with aplurality of write operations in the width direction of the track, sothe width is often different from the width of the normal data track.Consequently, when finding a sensitivity correction coefficient of theposition signal of the head, the width of the pattern for detectionfull-track profile must be adjusted to the width of the track in theburst part 43. In addition, when finding a sensitivity correctioncoefficient of the position signal of the head through convolutionintegral of a micro-track read-back profile and a rectangular function,the width of the rectangular function must be adjusted to the trackwidth of the actual burst part 43. To find a sensitivity correctioncoefficient of the position signal of the head more accurately, aplurality of patterns for detection full-track profile must be preparedat different radial positions of the head and a sensitivity correctioncoefficient of the position signal in each of those radial positions canbe calculated.

[0084] According to this embodiment, because a correction table iscreated for each of the heads mounted in the object magnetic recordingdisk apparatus, it is possible to improve the positioning accuracy ofthe head, thereby enabling the track density of the apparatus to beimproved more. The creation process of the correction tables can beautomated for the apparatus independently, so that the process can beincluded in the production processes easily. In addition, thosecorrection tables are created with use of the servo decoder circuitprovided in each apparatus, so the property variation of the servodecoder circuit can also be corrected at the same time.

[0085] Next, a description will be made for a method for detecting avariation of the head position signal with use of a pattern fordetection full-track profile with reference to FIG. 19.

[0086] In steps 1 to 3 shown in FIG. 19(A), the head is instructed toseek a track width measuring zone so as to follow the track, therebydetecting a full-track profile from a pattern for detection micro-trackprofile. Those processes are the same as those described in theembodiment 1. In step 4, a root sum (RMS value) is calculated from thedifference between the detected full-track profile and the referenceprofile. This reference profile is a measured value obtained from eachhead and written in the memory of the package board 17 or in part of themanagement area of the disk 12 beforehand, In step 5, the RMS value iscompared with the upper limit value. If the RMS value is less than theupper limit value, the state is judged to be normal, thus the processingis finished.

[0087]FIG. 19B shows a full-track profile measured at a normal time anda reference profile. After 20 times of measurement, the average of theRMS values was 8087 and the maximum and minimum values were 9610 and5954. Next, FIG. 19( ) shows a full-track profile measured when a headposition signal is varied and a reference profile. After 20 times ofmeasurement, the average of the RMS values was 20020 and the maximum andminimum values were 24155 and 16912. If the upper limit of the RMS valueis set to about 12000, it would be possible to detect a variation of thehead position signal surely. The RMS value described here is a unit usedinside computers and real values are not discussed.

[0088] Furthermore, a description will be made for a processing carriedout if the magnetized state of the read-back element is disturbed,thereby the output of the position signal is judged to be varied. If theretry count exceeds a predetermined value in step 6, it is judged thatthe head position signal is stabilized enough. Thus, a routine forregenerating the correction table of the position signal is called instep 7. The process for creating the correction table of the positionsignal is the same as that described in the embodiment 3.

[0089] If the retry count is judged to be within the predetermined valuein step 6, control goes to the retry processing. In this retryprocessing, the head is instructed to seek a zone where no user dataexists and a write operation (dummy write operation) is carried out soas to apply an external magnetic field to the read-back elementintentionally. After the dummy write operation, the same processes instep 2 and after are repeated. If the normal state is not restored afterthe dummy write operation, the sense current (Is) applied to theread-back element is increased or decreased, thereby improving theeffect of the dummy write operation. In stead of the dummy writeoperation employed for restoring the read-back element to the normalstate here, a more complicated process may be employed so as to improvethe effect of the retry.

[0090] Next, a description will be made for a method for detecting aproperty variation of the read-back element of the head with use of apattern for detection micro-track profile with reference to FIG. 20 Insteps 1 to 3 shown in FIG. 20(A), the head is instructed to seek a trackwidth measuring zone and follow up the track, thereby a micro-trackprofile is detected from the pattern for detection micro-track profile.The processes are the same as those described in the embodiment 2. Instep 4, the RMS value is calculated from between the detectedmicro-trackprofile and the reference profile. The reference profile is avalue measured for each head beforehand and written in the memory of thepackage board 17 or in part of the management area of the disk 12. Instep 5, the RMS value is compared with the upper limit value. If the RMSvalue is within the upper limit value, the state is judged to be normaland the processing is finished.

[0091]FIG. 20B shows a micro-track profile measured at a normal time andthe reference profile. After 20 times of measurement, the average of theRMS values was 1435. The maximum and minimum values were 1857 and 1040.Next, FIG. 20C shows a micro-track profile measured when a propertyvariation occurs in the read-back element and the reference profile.After 20 times of measurement, the average of the RMS values was 2821.The maximum and minimum values were 3598 and 2124. If the upper limit ofthe RMS value is set to about 2000, it would be possible to detect aproperty variation of the read-back element surely. The RMS valuedescribed here is a unit used inside computers and real values are notdiscussed.

[0092] Furthermore, a description will be made for a processing to beexecuted if the RMS value exceeds the upper limit value and themagnetized state of the read-back element is disturbed, thereby avariation is detected in the property. If the retry count exceeds apreset value in step 6, the read-back element head position signal ispossibly stabilized enough, so that a routine for learning the initialvalues of various parameters for the signal processing is called in step7.

[0093] If the retry count is still within the preset value in step 6,control goes to the retry processing. The retry processing is executedwith use of a method that lets the head seek a zone where no user dataexists, then execute a write operation (dummy write), thereby applyingan external magnetic field to the read-back element intentionally. Afterthat dummy write operation, the processings in step 2 and after arerepeated. If the normal state is not restored with a dummy writeoperation, the sense current (Is) applied to the read-back element isincreased/decreased, thereby improving the effect of the dummy writeoperation. In stead of the dummy write operation process employed tonormalize the read-back element in this embodiment, a more complicatedprocess may also be employed to improve the effect of the retry more.

[0094] According to this embodiment, therefore, because it is possibleto detect a phenomenon that the magnetized state of the read-backelement is disturbed, thereby the position signal output is varied, itis possible to avoid such a fatal error as overwriting an adjacent datatrack as a result of write operation offset from the target data track.Thus, the reliability of the magnetic recording disk apparatus has cometo be improved significantly. In addition, even when the position signaloutput is varied, the position signal correction table is recreated,thereby the same head positioning accuracy as that before the variationoccurs can be kept as is. Consequently, the track density of themagnetic recording disk apparatus has been improved successfully. Inaddition, because a property variation of the read-back element can bedetected only by reading back a detection pattern, it is possible toreduce such a recovery processing time as dummy write operation, etc.,thereby enabling the access performance of the magnetic recording diskapparatus to be improved more.

[0095] Furthermore, because it is possible to reduce error occurrence bycorrecting the non-linearity of the head position signal caused by thedegradation of the sensitivity at the end part and disturbance of themagnetizing direction of the head read-back element, the headpositioning accuracy can be improved more. In addition, because it ispossible to detect a property variation of the read-back element relatedto a variation of the head position signal surely and correct thevariation level, the reliability of the head positioning can be improvedsignificantly.

[0096] The present invention, therefore, can provide a magneticrecording disk apparatus that has increased the data track density inthe radial direction, thereby having improved both of the storagecapacity and the reliability successfully.

1. A magnetic recording disk apparatus, comprising: a magnetic recordingdisk medium having a plurality of tracks formed thereon in a concentriccircle pattern and a servo area formed on a part of each of a pluralityof said tracks and used to record a servo pattern; a magnetic headprovided with a read-back element and a write element; and a servodecoder for generating a head position signal from a servo patternformed on said magnetic recording disk medium; wherein a plurality ofpatterns are disposed in an area different from said servo area on saidmagnetic recording disk medium so as to be deviated respectively atleast more narrowly than the width of said read element of said magneticdisk head.
 2. A magnetic recording disk apparatus according to claim 1;wherein said magnetic recording disk medium has a data area in which adata pattern is written, and each of a plurality of said patterns has awidth equal to the track width of said data pattern.
 3. A magneticrecording disk apparatus according to claim 1; wherein said magneticrecording disk medium has a data area in which a data pattern is to bewritten, and each of a plurality of said patterns has a width narrowerthan the track width of said data pattern.
 4. A magnetic recording diskapparatus according to claim 1; wherein a plurality of said patterns aredisposed on two or more tracks.
 5. A magnetic recording disk apparatusaccording to a claim 2; wherein a plurality of said patterns aredisposed on two or more tracks.
 6. A magnetic recording disk apparatusaccording to claim 3; wherein a plurality of said patterns are disposedon two or more tracks.